Solar Power

May 3rd, 2010 by Tim Delhey Eian

by Peter Henry, Energy Concepts

As sustainable design moves out of its infancy and tries to establish norms and standards for new construction, one of its central challenges is how to create energy that can power an entire house–and where possible–feed any surplus back to the grid.

Energy Concepts (ECI) was contacted early on as the Passive House in the Woods project concepts were being explored. As 2009 Focus on Energy Market Provider of the Year, ECIʼs veteran engineer Craig Tarr has the kind of experience and technical background to make a “carbon neutral” building become “carbon negative”–that is, a building that produces more energy than it consumes.

There is nothing more sustainable than creating a building that is a net producer of energy rather than a consumer. Given the problems of fossil fuel electricity production, this is likely to be the “gold standard” in sustainable design going forward. Quite simply: if we are not part of generating societyʼs solutions, than we are part of its problem; or at least, are certainly subject to its problems.

With that in mind, ECI set out to design a system that would meet a high standard: producing at least as much energy as it consumes. Passive House in the Woods is an all electric home, so the issues were reduced to providing electricity. But, because it is much cheaper to heat water with the sun than to produce electricity from the sun to heat water, a secondary system to provide solar hot water was planned.

Generating electricity in a rural area comes down to two choices: wind or solar. In this case, since the electric needs were fairly modest and the wind resource not particularly abundant, a solar photovoltaic system was the clear preference.

ECI and its installation partner Steiner Plumbing/Heating/Electric of River Falls, have developed a specialty in solar PV Top of Pole Mounts (TOP). Essentially, rather than using a buildingʼs roof for mounting PV panels, the TOP uses an 8ʼ x 8ʼ steel beam anchored in cement and then mounts a rack of panels on top of that. The system maximizes efficiency when it is paired with a dual axis tracker, as explained in this post about how TOPs are actually installed.

Tarr and the other engineers and contractors examined the likely electric use at Passive House in the Woods and determined that while meeting as much as 90% of the buildingʼs overall electric use, the TOP mount would likely fall short of zeroing out the bill completely. So, an additional four SunPower 210 panels were mounted, along with the solar hot water panel, a 4ʼ x 10ʼ Solar Skies SS40, on the buildingʼs roof.

Letʼs take a moment to talk about solar PV panels. SunPower panels were selected for this site because they are hands down the best, most productive solar panel commercially available. Likely you will hear a lot of hew and cry about solar innovations– nano-solar, thin-film solar, Chinese panels at $1.00 a watt –but what needs to be understood is that, as a long-term investment that will provide an essential

service to a house, solar PV is not about messing around with things experimental or cheap. The last thing any homeowner wants or needs is to be left without electricity after a long day at work. Thatʼs why SunPower is far and away the best solar panel in todayʼs market. At 31” x 61” the panels mounted on the TOP system produce 230 watts instantaneously– at least. And, as has been verified in independent 3rd party testing, SunPower panels often outperform their nameplate rating–meaning they produce more than they are rated to produce. Thatʼs a new spin on the old idea of “free energy”.

But, the point is this about solar PV: a homeowner only has so much space, either on their roof or in their yard, and they have to produce as much power as they can. Given that, the best, most powerful and reliable way to do that is to use SunPower modules. And thatʼs what the best and brightest clearly understood when designing the electric generation system for Passive House in the Woods.

So, for the electric needs of Passive House, there are 16 — 230 watt panels mounted on the Top of Pole system, governed by a dual axis tracker which is constantly maximizing production by aiming the panels directly into the sun. As the sun moves, the panels track the sun; as the season changes sun angle, the panels adjust as well.

The 16-panel system should produce in the range of 6,000 kWhs annually. But, because Passive House set a high standard of being completely carbon neutral, if not carbon negative, an additional 4 SunPower 210s were racked up on the roof. That will provide at least another 1,000 kWhs annually, thus putting the Passive House in the Woods over their anticipated power needs on an annual basis.

By the way, generating electricity with solar is not, right now, competitive with current generation methods. Meaning: yes, it is cheaper to sit back and allow the power company to provide you with electricity. The problem with that though is, we donʼt really understand all the costs that are accruing to the environment and the human population as a result of burning coal. If we truly understood those costs, and could price them, the odds are good that solar would not only be competitive with coal, but actually outperform coal. So, while a system like the one described here is in excess of $50,000, before generous State and Federal incentives kick in and knock the costs under $30,000, the real question should not be about the costs of solar: it should be, what are the real costs of coal? And are we leaving those costs for future generations to pay?

Next time: understanding the solar hot water system at Passive House in the Woods.


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